Wednesday, January 18, 2012

Difference between SCADA and BMS (Building Management System)

SCADA is interface software to control and data acquisition, installed on personal computers and applied with PLCs or industrial automation controls. They are usually developed by product manufacturers of automation, such as Siemens, Rockwell, Invensys, or by some independents (frequently bought by bigger automation industries, such as Intouch, Wonderware, Citect,), and sometimes by persons who like their own interfaces in Delphi, Visual C, etc. Communications are performed over dedicated buses such as Fieldbus, Profibus, Modbus, Industrial Ethernet and the drives, sensors, motor controllers are constructed to swap over with the PLCs.

Building Management Systems (BMS) are a parallel industry. The components are different, the manufacturers are more lighting industrials such as Carrier, Trane, Homneywell, and HVAC. The standard of BMS is different with SCADA. BMS is using different communication protocols such as, BACNET, EIB, LonWorks. Usually, industrial standards will control higher voltages, utilize more power, and use smaller wire gauge than automation of building.

Converting to a system of PLC type is not simple as one would think. The controller of VAV got multiples function built in with sensor and two temperature input. The controller of VAV doesn’t have a clock so you require another supervisory controller to control the function of scheduling.

A characteristic setup of BMS is as below:
• Top Level usually Ethernet is PC running HMI function
• Mid Level this works as the bridge between the lower and upper network. The function as timer, scheduling and Supervisory controller running script function.
• Lower Level usually on some RS485 type of network with either open or proprietary protocol.

Some of the lower level device such as controller of VAV can function well all on its own. The most difference between a system of PLC SCADA and a BMS is an execution speed. BMS is slower.